Device for utlilizing geothermal heat and method for operating the same

ABSTRACT

An apparatus and a method for using geothermal energy include the use of at least a first conduit, through which a working substance is carried downward into the interior of the Earth, at least one second conduit, through which the working substance is carried upward, in the direction of the surface of the Earth, with the first and second conduits form a closed system relative to the soil, wherein the working substance is carried downward into the interior of the Earth, and the throttling region throttles the largely liquid working substance upstream, in the flow direction, of the throttling region to a vaporization pressure, so that downstream of the throttling region the working substance is largely completely vaporizable.

BACKGROUND OF THE INVENTION

The invention is based on an apparatus for using geothermal energy andmethod of generating it.

A heat flow, flowing from the interior of the Earth, can be ascribed toan extent of about 80% to the decay of radioactive isotopes in rocks,and about 20% to the primordial heat generated in the creation of theEarth. The temperature from the Earth's surface to the interior of theEarth increases by about 30° C. every 1000 meters. In the vicinity ofgeothermal anomalies, greater temperature increases can occur, forinstance because of a geographic closeness to hot magma chambers(intrusions) in the crust of the Earth, flows of deep-seated bodies ofwater, and so forth. Such regions are especially preferred for utilizingthe geothermal energy.

The geothermal energy can be stored in various substances, fundamentallyin water vapor, water, and/or hot strata of rock.

Stored water vapor is usually located in the vicinity of activevolcanoes and highly fissured or water-bearing bedrock. The vapor can becarried to the Earth's surface and—after an often-necessary separationof entrained water—used to generate electricity. However, usable vaporsources exist in only a few regions.

The energy stored in the hot water in strata of the Earth are as a rulereached by an apparatus known as a doublet. The doublet has a feed bore,through which the hot water from the various strata of the Earth can bepumped to the Earth's surface. To prevent the hydrostatic pressure inthe strata from dropping over time, and to avoid lessening the inflow ofhot water and in particular to enable better utilization of the heat ofthe rock, the cooled water is returned to the corresponding strata ofthe Earth via an injection bore. From the injection bore, the water canflow through the rock to the feed bore and is heated in the process. Thewater pumped out of the strata of the Earth is as a rule used for spaceheating.

For tapping the energy stored in hot layers of rock, a so-called hot dryrock process is known. In this process, in a first method step a firstdeep hole is drilled down to about 5000 meters. Via the deep hole, wateris forced at high pressure to a depth of about 5000 meters into therock, causing cracks to form in the rock. With a second deep hole, at adistance of about 500 meters, the region where the cracks have formed isdrilled into. Next, water can be pumped into the rock via one deep holeand carried through the cracks to the second deep hole and then pumped,heated, to the Earth's surface via the second deep hole. To avoidexpensive dry holes, the cracks in the rock have to be located. At adepth of 5000 meters, this is especially difficult and complicated.

Another apparatus of this generic type is known that has threeconcentrically arranged pipes, specifically a so-called outer descendingpipe, a cladding tube, and an inner riser pipe. Cold water is pumpeddownward into the interior of the Earth through the descending pipe,heated, and having been heated, is pumped upward through the riser pipe.An annular gap with air between the riser pipe and the cladding tubeserves as an insulator between the outer descending pipe and the innerriser pipe. The pipes are surrounded on the outside, toward the soil, bya water-impermeable suspension, for instance of betonite. A masstransfer with the soil is avoided. However, the efficiency forgenerating electrical energy is low.

U.S. Pat. No. 4,644,750 discloses an apparatus of this generic type, inwhich a working substance is pumped downward into the ground via a firstpipe into a deep hole and upward via capillaries. By capillary action,the attempt is made to keep external power for pumping the workingsubstance upward from below as slight as possible

SUMMARY OF THE INVENTION

The object of the invention is to refine the apparatus of this generictype and in particular to create an apparatus and a method with which,economically and in a way that can be achieved simply from atechnological standpoint, a circular process for recovering energy canbe created, which is maintained without external power or with only veryslight external power.

The invention is based on an apparatus for using geothermal energy,having at least a first conduit, through which a working substance iscarried downward into the interior of the Earth, and having at least onesecond conduit, through which the working substance is carried upward,in the direction of the surface of the Earth, and the first and secondconduits form a closed system relative to the soil.

It is proposed that the working substance is carried downward into theinterior of the Earth, and the throttling region throttles the largelyliquid working substance upstream, in the flow direction, of thethrottling region to a vaporization pressure, so that downstream of thethrottling region the working substance is largely completelyvaporizable. The working substance can advantageously be carrieddownward in the liquid state and upward in the gaseous state, at lowerdensity. The liquid pressure that builds up, or the force of gravityacting on the liquid, can be utilized for a requisite pressure elevationin a clockwise cycle process, and as a result an especially highefficiency can be achieved, especially in the generation of electricalenergy. In principle, however, a pump can also be used to generate arequisite pressure upstream of the throttling region; the pump acts toreinforce the liquid column or generates the requisite pressure byitself.

Once the working substance downstream of the throttling region hasvaporized extensively, and advantageously completely, it flows upward tothe Earth's surface. During operation of the apparatus, it is possibleto avoid introducing an external power, in particular pumping power,which thus enhances the efficiency. A slight pressure drop isestablished in the second conduit, from bottom to top in the gas column.At the Earth's surface, the working substance in vapor form has a muchhigher pressure than in an initial state of the process, and this canespecially advantageously be used to generate electrical energy. Thethrottling region can be formed by one throttling point, oradvantageously by a plurality of throttling points, which are disposedspaced apart from one another in the flow direction. When there are morethan one throttling point, an especially high pressure can be achievedin the upper region of the second conduit.

In a further feature of the invention, it is proposed that a compressor,by way of which the working substance is compressable upstream of thethrottling region, is disposed downstream in the flow direction of thesecond conduit. The throttling region can especially advantageously bedisposed in the upper region of the first conduit, and a largetemperature difference between the working substance and the interior ofthe Earth, and as a result a good heat transfer to from the interior ofthe Earth to the working substance, can advantageously be achieved overthe entire first conduit. The energy delivered from the interior of theEarth can advantageously be utilized for vaporization, at a largelyconstant vaporization temperature of the working substance. In thesecond conduit, the working substance largely has the same temperatureas in the first conduit, as a result of which an insulation between theconduits can be omitted. To recover a high quantity of heat, even aslight hole depth can already suffice.

The throttling region can fundamentally be formed by one or morethrottling points that appear suitable to one skilled in the art.Especially advantageously, however, at least one throttling point isformed by at least one pipe. Given an adequate throttling action, arelatively low flow velocity through the throttling point and thus lowwear and a long service life can be achieved.

In one feature of the invention, it is proposed that the first andsecond conduits communicate to form a closed system; that is, theycommunicate in closed fashion not only underground but also aboveground. The working substance can be prevented from escaping from thesystem, and a working substance with which an especially high efficiencycan be achieved at the lowest possible cost can advantageously beemployed.

If the working substance has a lower boiling temperature than water,then in comparison to water-driven apparatuses, the working substancecan already be made to vaporize at lesser depths or lower temperatures,so that drilling costs in particular can be saved. Conventionalrefrigerants, such as ammonia in particular, are advantageously suitableas the working substance.

To reduce the flow velocity in the first conduit and to increase theservice area and thereby improve the heat transfer to the workingsubstance, at least one element deflecting the working substance isadvantageously placed at least downstream of the throttling region inthe first conduit. Filler bodies, which deflect the working substance,can advantageously be introduced into the first conduit. In a furtherfeature, it is proposed that instead of filler bodies, at least onepathway extending spirally downward is introduced, by way of whichpathway the working substance is carried against the outer wall of thefirst conduit, as a result of which an advantageous film vaporization onthe outer wall of the first conduit can be achieved. The pathway can bemade from various materials; for instance, the pathway can be formed bya sheet-metal part, or it can also be embodied integrally with a conduitwall. Preferably, the pathway does not have any sealing function in theconduit.

In one feature of the invention, the first and second conduits aredisposed in a deep hole that is lined imperviously, and the workingsubstance is carried through an inner pipe downward in the radiallyouter region inside the deep hole and upward in the radially innerregion of the deep hole. Additional deep holes can thus be dispensedwith and the attendant costs eliminated. Furthermore, the conduits canbe made to communicate in closed fashion underground in an especiallysimple, inexpensive way. In principle, however, the working substancecan also be carried downward via one or more deep holes and upward viaone or more other deep holes separate from the first group.

DRAWING

Further advantages will become apparent from the ensuing description ofthe drawing. The drawing shows one exemplary embodiment of theinvention. The drawing, description and claims include numerouscharacteristics in combination. One skilled in the art will expedientlyassess the characteristics individually as well and put them together tomake useful further combinations.

DESCRIPTION OF THE DRAWINGS

FIG. 1, a schematic illustration of an apparatus according to theinvention; and

FIG. 2, method sequences in a graph of pressure and enthalpy; and

FIG. 3, a variant of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an apparatus according to the invention for usinggeothermal energy, having a first conduit 10 through which a workingsubstance 12 is carried downward into the interior of the Earth, andhaving a second conduit 14 through which the working substance 12 iscarried upward in the direction of the Earth's surface. The firstconduit 10 is formed by a first outer pipe 52, which is inserted into adeep hole 36 and lines the deep hole 36 imperviously toward the outside.The outer pipe 52 is tightly closed at its face end on the lower end.The second conduit 14 is formed by an inner pipe 46, disposedconcentrically to the outer pipe 52 in the radially inner region of thedeep hole 36. The inner pipe 46 is surrounded by a cladding tube 56,which for insulation purposes encloses an annular gap 58 with airrelative to the inner pipe 46 and which defines the first conduit 10radially toward the inside. The first and second conduits 10, 14 areconnected jointly to an equipment system 60 to make a closed system, sothat the ammonia used as the working substance 12 cannot escape to theoutside.

According to the invention, the first conduit 10 has a throttling region16, with three throttling points 22, 24, 26 disposed in line with oneanother in the flow direction. The throttling points 22, 24, 26 are eachdisposed spaced apart from one another and are each formed by arespective pipe 28, 30, 32 secured in a flange 40.

When the apparatus is constructed, the outer pipe 52, cladding tube 56and inner pipe 46 are already introduced jointly and concentrically insegments as the deep hole 36 is drilled. The segments are tightly joinedto one another by welding at the axial abutting points. In principle,however, the segments can also be tightly joined by various methods thatappear useful to one skilled in the art, by material engagement,positive engagement and/or nonpositive engagement.

The flange 40 can be secured between the outer pipe 52 and the claddingtube 56 by various methods that appear suitable to one skilled in theart. Especially advantageously, however, the flange will be solidlywelded to the outer pipe 52 and the cladding tube 56 before the pipes46, 52, 56 are introduced into the deep hole 36. To prevent the firstconduit 10 from becoming soiled during drilling, and to prevent drillingsludge and/or a suspension from entering the first conduit 10, the firstconduit 10 in the bottommost segment is closed with a steel plate 54 onthe axial face end even before being introduced into the deep hole 36. Adrill head of a drilling apparatus, not shown in detail, can be passedupward and downward in the collapsed state through the inner pipe 46.The second conduit 14 can be cleaned after the drilling process has beenconcluded. Once the deep hole 36 is finished, the inner pipe 46 istightly closed off from the soil on its downward-pointing axial face endby a plastic plate 42. In addition, the axial face end of the inner pipe46 can be tightly closed off from the soil by any methods appearingsuitable to one skilled in the art, for instance by compound filling,and/or by press-fitting of a teflon body, making it possible to create anonpositive and positive closure. It is also possible for the claddingtube 56 and/or the inner pipe 46 not to be introduced into an outerpipe, which is tightly closed on its downward-pointing face end, untilafterward.

Before the inner pipe 46 and the cladding tube 56 are introduced,openings 136, 138 or bores are made in their bottommost segments. Theopenings 138 in the inner pipe 46 are then closed again by nonpositiveand positive engagement or in some suitable way before the introduction,so that on the one hand they reliably prevent the voids between thepipes 46, 52, 56 from becoming contaminated on the other hand theybecome open again because of the pressure difference, caused uponfilling with ammonia, between the first conduit 10 and the secondconduit 14. Either the openings 136, 138 or only the openings 138 can,however, also be made later, after the pipes 46, 52, 56 are introduced,or they can be closed with substances that chemically dissolve inammonia but are resistant to the substances used in drilling the hole.

At the beginning of putting the apparatus into operation, all the valves72, 74, 76 and 84-128, 140 are opened. In order to fill the firstconduit 10 completely with liquid ammonia as fast as possible, liquidammonia is introduced into the apparatus at a pressure of about 25 barvia a line 64 and via the second conduit 14. If there is only onethrottling point in the first conduit 10, then the apparatus can also befilled via the first conduit 10. The apparatus is ventilated via lines68, 70, which empty into a water bath, not identified by referencenumeral. Once air bubbles are no longer rising upward in the water bath,the valves 72, 74 in the lines 68, 70 can be closed. Once a certain filllevel is detected by a fill level gauge 78 in a condensate reservoir 66,the valve 76 in the line 64 is closed. The valves 94, 96 and 98 are alsoclosed.

Next, via a jet pump 50, which is supplied with ammonia from thecondensate reservoir 66 by a driving jet pump 80, the pressure p in thesecond conduit 14 is reduced, and as a result the ammonia in the secondconduit 14 is vaporized. The ammonia pumped by the jet pump 50 iscondensed in a heat exchanger 130 and returned to the condensatereservoir 66.

If a temperature that indicates that the ammonia in the second conduit14 has vaporized completely or at least extensively is detected at ameasurement point 82, the driving jet pump 80 is switched off, and thevalves 84, 86 are closed. In order to dissipate heat solely via a heatexchanger 132 to a consumer, not identified by reference numeral, onlythe valve 94 is then opened. To generate electrical energy with aturbine 134 and a generator 62, the valves 96 and 98 are opened.

During the operation of the apparatus, liquid ammonia from thecondensate reservoir 66 is carried into the first conduit 10 via thevalves 126 and 92. In a first region 48 of the first conduit 10, theammonia is liquid. From the starting point P1 in the upper region of theliquid column that develops in the first conduit 10, the pressure pincreases toward the bottom as a consequence of gravity, andspecifically the pressure p at point P1 is about 25 bar, while at pointP2, at a depth of 1650 meters, it is about 100 bar (FIG. 2). Thepressure p is throttled by the throttling point 22 at the depth of 1650meters. Downstream of the throttling point 22, the pressure p at P3 isabout 45 bar. From P3 to P4, the pressure p increases as a consequenceof the gravity in the liquid column, and at P4, at the depth of 2850meters, it amounts to about 105 bar. From P4 to P5, the pressure p isthrottled by the second throttling point 24 at the depth of 2850 meters.From P5 to P6, the pressure p increases to about 105 bar, at the depthof 3850 meters. From P6 to P7, the pressure p is throttled by the thirdthrottling point 26, at the depth of 3850 meters, to a vaporizationpressure 18 of about 60 bar. Between the throttling points 22, 24, 26,heat from the ground is continuously supplied to the ammonia, and as aresult the enthalpy h increases between the throttling points 22, 24,26.

The enthalpy h increases from P7 to P8 at a constant pressure p as aconsequence of the pressure energy, from P8 to P9 as a consequence ofthe cooling down of the superheated ammonia, and from P9 to P10 as aconsequence of the supply of heat from the ground. To achieve a goodheat transfer from the ground to the ammonia, filler bodies 34 (FIG. 1)are introduced downstream of the bottommost throttling point 26 in thefirst conduit 10. At point P10, at a depth of about 4600 meters, theammonia has vaporized completely and can flow from the first conduit 10into the second conduit 14 via the openings 136, 138 in the claddingtube 56 and the inner pipe 46, respectively (FIG. 1). To prevent theammonia gas in the annular gap 58, between the cladding tube 56 and theinner pipe 46, from rising to the top, the annular gap 58 is closed offby a stopper element 38 above the openings 136, 138, in the direction ofthe Earth's surface. The stopper element 38 is secured, like the flange40 of the throttling points 22, 24, 26, before the introduction into thedeep hole 36. The ammonia gas flows upward to the Earth's surface in thesecond conduit 14. The pressure p and the enthalpy h decrease from P10to P11. At point P11, the ammonia gas is at about 40 bar, that is, about15 bar more than at the starting point P1. The energy excess from P11 toP1 can be utilized to dissipate heat to consumers—P11-P12-P13-P1—or canbe utilized to generate electrical energy and to dissipate heat—P11-P12a-P1. The result is a closed, clockwise cycle process. Instead ofoperating the apparatus with a plurality of throttling points 22, 24,26, it can also be operated with only one throttling point. In FIG. 2, adashed line indicates a method sequence of an apparatus with only onethrottling point. In comparison to a plurality of throttling points, theammonia is throttled to a lower vaporization pressure 20.

For regulating capacity, the inflow from the condensate reservoir 66into the first conduit 10 can be regulated via the valve 126. The liquidcolumn should not drop below the first throttling point 22. To turn offthe apparatus, either the supply from the condensate reservoir 66 to thefirst conduit 10 can be disrupted, or the liquid ammonia can be pumpedout of the condensate reservoir 66 into the inner pipe 46 via a pump 44,as a result of which the apparatus can be switched off especiallyquickly. The pump 44 can also be used to resume operation.

FIG. 3 shows a variant of the apparatus shown in FIG. 1. Components thatremain essentially the same are all identified by the same referencenumerals. The apparatus has a first conduit 10, through which theworking substance 12 is carried downward into the interior of the Earth,and a second conduit 14, through which the working substance 12 iscarried upward, in the direction of the Earth's surface. The firstconduit 10 is formed by an outer pipe 52, which is inserted into a deephole 36 and lines the deep hole 36 imperviously toward the outside. Theouter pipe 52 is tightly closed at its face end on the lower end. Thefirst conduit 10 is bounded radially inward by an inner pipe 152, whichis disposed concentrically with the outer pipe 52 and forms the secondconduit 14. A pathway 35 extending spirally downward is placed in thefirst conduit 10, between the pipes 52 and 152; it deflects the workingsubstance 12 against the outer wall of the first conduit 10 and againstthe inside surface of the outer pipe 52, as applicable. The pathway 35furthermore serves as a spacer between the pipes 52 and 152. The pathway35 can extend over the entire length of the conduit 10 or canadvantageously be disposed in segments of various lengths, between whichthere is a spacing. The pathway 35 does not take on any sealing functionin the first conduit 10. The first and second conduits 10, 14 areconnected jointly to an equipment system 154 to form a closed system, sothat the ammonia used as the working substance 12 cannot escape to theoutside.

The ammonia in vapor form flowing upward in the second conduit 14 iscompressed in a compressor 142 downstream of the second conduit 14,specifically to about 25 bar, and in the process is heated orsuperheated to approximately 130° C.

In a heat exchanger 144 downstream of the compressor 142, heating wateris heated in three phases, specifically in a first phase by cooling ofthe ammonia down to a temperature of condensation, in a second, primaryphase by condensation of the ammonia, and in a third phase by coolingdown of the condensate. The heating water is further heated, in anexhaust gas heat exchanger 150 downstream of the heat exchanger 144, byexhaust gases 146 from a motor 148 of the compressor 142.

Downstream of the heat exchanger, the working substance 12 is about 45°C., and downstream of the heat exchanger 144 it is carried via athrottling region 15, disposed in the upper region of the first conduit10, or via a throttling point, and in the process is throttled fromabout 25 bar to a vaporization pressure of about 4 bar. The throttlingregion 15 or a throttling point can also be disposed in a line upstreamof the first conduit 10.

As a result of the throttling, the working substance 12 is cooled downto about 0° C. The liquid working substance 12 is carried through thepathway 35 downward and by centrifugal force against the outer wall ofthe first conduit 10, where film vaporization occurs. The vaporizedworking substance 12 is carried downward in the first conduit 10 andupward in the second conduit 14 by a resultant total flow. In the firstand second conduits 10, 14, the working substance 12 essentiallymaintains its vaporization temperature of approximately 0° C. Anespecially good heat transfer from the interior of the Earth to theworking substance 12 can be achieved, and it is furthermore possible todispense with an insulation between the first conduit 10 and the secondconduit 14.

What is claimed is:
 1. An apparatus for using geothermal energy and forrecovering energy, comprising at least a first conduit through which aworking substance is carried downwards into an interior of the Earthinto a deep hole, at least one second conduit through which the workingsubstance is carried upwards in a direction of a surface of the Earth,said first and second conduits forming a closed system relative to asoil; at least one throttling region through which the working substanceis carried downwards into the interior of the Earth, so that the workingsubstance is also in heat exchange with its surroundings as it is beingcarried downwards, said throttling region throttling the workingsubstance which is substantially a liquid working substance upstream ina flow direction of said throttling region to a vaporization pressure,so that downstream of said throttling region the working substance issubstantially completely vaporizable.
 2. An apparatus as defined inclaim 1, wherein said throttling region is formed so as to elevate apressure upstream of said throttling region, and a force of gravityacting on a liquid column, dammed up upstream of said throttling region,of the working substance is utilized.
 3. An apparatus as defined inclaim 2; and further comprising a plug disposed upstream of saidthrottling region for elevating the pressure.
 4. An apparatus as definedin claim 1, wherein said throttling region is formed by a first and atleast one second throttling point which is disposed at a spacing in theflow direction from said first throttling point.
 5. An apparatus asdefined in claim 1; and further comprising a compressor by which theworking substance is compressible upstream of said throttling region,said compressor being disposed downstream in the flow direction of saidsecond conduit.
 6. An apparatus as defined in claim 5; and furthercomprising at least one heat exchanger, said compressor being disposedupstream in a flow direction of said at least one heat exchanger.
 7. Anapparatus as defined in claim 6; and further comprising a motor thatdrives said compressor; and an exhaust gas heat exchanger arranged sothat the exhaust gasses of said motor are carried through said exhaustgas heat exchanger.
 8. An apparatus as defined in claim 1, wherein saidthrottling region is disposed in an upper region of said first conduitwhich extends downwardly.
 9. An apparatus as defined in claim 1, whereinsaid throttling region has at least one throttling point which is formedby at least one pipe.
 10. An apparatus as defined in claim 1, whereinsaid first and second conduits communicate to form the closed system.11. An apparatus as defined in claim 1, wherein the apparatus is formedso that it uses the working substance which has a lower boilingtemperature at the same pressure than water.
 12. An apparatus as definedin claim 11, wherein the working substance is ammonia.
 13. An apparatusas defined in claim 1; and further comprising at least one elementdeflecting the working substance at least downstream of said throttlingregion in said first conduit.
 14. An apparatus as defined in claim 13;and further comprising filler bodies that deflect the working substanceand are introduced into said first conduit.
 15. An apparatus as definedin claim 13; and further comprising at least one pathway extendingspirally downwards and introduced into said first conduit, so that theworking substance is carried by said pathway against an outer wall ofsaid first conduit.
 16. An apparatus as defined in claim 1, wherein saidfirst and second conduits are disposed in a deep hole that is linedimperviously; and further comprising an inner pipe through which theworking substance is carried downwardly in a radially outer regioninside the deep hole and upwards in a radially inner region of the deephole.
 17. A method of operating an apparatus comprising at least a firstconduit through which a working substance is carried downwards into aninterior of the Earth into a deep hole, at least one second conduitthrough which the working substance is carried upwards in a direction ofa surface of the Earth, said first and second conduits forming a closedsystem relative to a soil; at least one throttling region through whichthe working substance is carried downwards into the interior of theEarth, so that the working substance is also in heat exchange with itssurroundings as it is being carried downwards, said throttling regionthrottling the working substance which is substantially a liquid workingsubstance upstream in a flow direction of said throttling region to avaporization pressure, so that downstream of said throttling region theworking substance is substantially completely vaporizable, the methodcomprising the steps of throttling the working substance which in afirst region of the first conduit is substantially liquid, in a secondregion to a vaporization pressure; subsequently vaporizing the workingsubstance substantially completely; and carrying it in a vapor stateupwards in the second conduit.
 18. A method as defined in claim 17; andfurther comprising throttling the working substance in the second regionby a first and at least a second throttling point to the vaporizationpressure in at least two steps; and supplying heat between thethrottling points to the working substance.
 19. A method as defined inclaim 17; and further comprising supplying the working substance via thesecond conduit when the apparatus is put into an operation.
 20. A methodas defined in claim 19; and further comprising reducing a pressure inthe second conduit when the apparatus is put into operation after beingfilled, with a pump; and vaporizing the working substance in the secondconduit.